The invention deals with techniques and arrangements for removing and neutralizing harmful emissions from industrial waste gases, such emissions constituting acidic components such as oxides of nitrogen and sulphur.
As is well-known, air pollution arising from waste gases from industrial plants are of major concern to modern technology, both from the point of view of personal health and also, to some extent, from the point of view of economics. The harmful acidic pollutants in such industrial waste gases may include, e.g. oxides of nitrogen resulting from the manufacture of nitric acid; silicon tetrafluoride, a waste product resulting from the manufacture of superphosphates; and oxides of sulphur, which along with certain nitrogen oxides, originate in the manufacture of sulphuric acid. Additionally, emissions from thermal power stations using low-grade fuel may contain up to 5% by weight of sulphur constituents. Cumulatively, such emissions cause the overall content of acidic pollutants in waste gases to amount to millions of metric tons yearly in some industralized countries.
Several scrubbing techniques are presently known for removing and neutralizing such acidic components of industrial waste gases. One such method employs, as an active scrubbing agent, aqueous solutions of carbonates of alkaline metals. This technique has the disadvantage of requiring a large consumption of industrial steam.
In the improved technique described, e.g., in U.S. Pat. No. 3,505,008, flue gases are filtered through a thin porous bed made up of crystals of a hydrogen carbonate of an alkali metal at temperatures between 0.degree. and 125.degree. C. Further, as described in U.S. Pat. No. 3,589,863, sulphur dioxide constituents of waste gases are removed by passing the gas to be treated through a stable bed containing particles of hydrogen carbonates of alkaline metals that have a porosity of 10 - 60% and a grain size of 1.6 - 19 mm.
Unfortunately, such techniques require a high investment cost and are not particularly effective when the concentration of the acidic pollutants in the waste gas is lower than, say, 0.2 volume percent; by contrast, in practice, large amounts of gases are produced having a substantially lower concentration of such components. Additionally, it is extremely expensive, difficult and cumbersome in such arrangements to replace the spent active materials in the bed.